Polycrystalline silicon is used as a raw material of monocrystalline silicon for semiconductors and a raw material of monocrystalline silicon for solar cells. High electric characteristics are required to the monocrystalline silicon, and therefore an amount of carbon which is an impurity exerting an adverse effect on the electric characteristics is desired to be reduced as much as possible.
Production processes for polycrystalline silicon include a process in which it is produced by reduction of silicon tetrachloride (SiCl4) using a metal reducing agent. To cut down an amount of carbon contained in polycrystalline silicon produced in the production process, it is important to reduce a trace amount of carbon-containing silicon-chlorine compounds (hereinafter referred to as organic chlorosilanes) contained as impurities in silicon tetrachloride. Accordingly, a purification method comprising separating and removing organic chlorosilanes from silicon tetrachloride by distillation has so far been carried out. However, even though the method is generally very expensive, such as requiring installation of a lot of multistage distillation towers, it is difficult to sufficiently separate and remove organic chlorosilanes.
In order to solve the problem, a method in which the number of distillation towers is decreased and comprising bringing silicon tetrachloride into contact with an adsorbent to separate and remove organic chlorosilanes is proposed (refer to, for example, a patent literature 1). The adsorbents include silica gel, activated carbon and molecular sieves and the like each having a large specific surface area. However, the adsorbents have the problem that an adsorbing ability of organic chlorosilanes is reduced while using and that the waste is generated due to exchanging the adsorbents.